What were the four factors of a job's income covered in the book 'freakonomics'

I read the book freakonomics last week and remember when he was doing a story about prostitution that there were four factors in how well a job payed.

Supply of workers
How undesirable the job is
The demand for the job

And I forget the last one, does anyone know what it was? His example of this type of thing was prostitution, which pays very well. There is a very small supply of people willing to be prositutes, it is an undesirable job and there is alot of demand, as a result income is very high.

I’m just guessing here, maybe barriers to entry (like education or certification)? Not really needed for prostitution.

Yeah I think that was it, the specialization needed to perform a task.

Prostitution does tend to cut out about 50% of people though.

You mean, men?

Well, they would serve a different market, is all.

A different, probably much smaller, market.

Wesley Clark: His example of this type of thing was prostitution, which pays very well.

Did he provide a cite for that claim? I don’t think of streetwalking as a particularly high-income profession, and as I understand it, a good deal of many prostitutes’ income goes as overhead to some kind of boss, madam, or pimp in exchange for “protection” and bribery.

I’d think that criminalization would have a distorting effect on the idealized free-market operation of the “four factors” you mention.

I don’t have my copy of the book on hand, but if I remember right, he was comparing high-end callgirls to low-end streetwalkers, and comparing both to flipping hamburgers.